Radical curable adhesive composition, and polarizing plate and optical member comprising same

ABSTRACT

The present invention relates to a radical-curable adhesive composition including a (A) radical-polymerizable compound that includes at least one hydrophilic functional group in the molecule in greater than 30 parts by weight and less than or equal to 93 parts by weight; a (B) multifunctional (meth)acryl-based compound in 5 to 40 parts by weight; a (C) phosphate compound that includes one or two (meth)acrylic groups in the molecule in 1 to 40 parts by weight; and a (D) radical initiator in 0.5 to 20 parts by weight, with respect to 100 parts by weight of the radical-curable adhesive composition, and a polarizing plate and an optical member including the radical-curable adhesive composition.

TECHNICAL FIELD

The present disclosure relates a radical-curable adhesive composition,and a polarizing plate and an optical member including the same, and inparticular, to a radical-curable adhesive composition having excellentwater resistance while having excellent adhesive strength between apolarizer and a protective film, and a polarizing plate and an opticalmember including the same.

BACKGROUND ART

Polarizing plates having a structure in which a protective film islaminated on one or both surfaces of a polarizer formed with a polyvinylalcohol (hereinafter, referred to ‘PVA’)-based resin dyed with dichroicdye or iodine using an adhesive have been commonly used. Triacetylcellulose (TAC)-based films have been normally used as a polarizingplate protective film in the art, however, such TAC films have a problemof being readily deformed in high temperature and high humidityenvironments. Accordingly, protective films made of various materialscapable of replacing TAC films have been recently developed, and forexample, a method of using polyethylene terephthalate (PET), acycloolefin polymer (COP), and an acryl-based film either alone or as amixture thereof has been proposed.

Herein, aqueous adhesives formed with an aqueous solution of a polyvinylalcohol-based resin are normally used as an adhesive used to attach thepolarizer and the protective film. However, aqueous adhesives have aproblem in that the use is limited depending on the material of a film,since adhesive strength is weak when acryl-based films or COP films andthe like are used as the protective film instead of TAC. In addition tothe problem of adhesive strength defects depending on the materials, theaqueous adhesive also has problems in that curls are generated in apolarizing plate due to a drying process of the aqueous adhesive, andinitial optical properties are degraded when materials of the protectivefilm used on both surfaces of a PVA element are different. Moreover, adrying process is absolutely required when the aqueous adhesive is used,and differences in moisture permeability, heat expansion and the likeoccur in the drying process leading to a problem of a defect rateincrease. As an alternative to solve the problems described above,methods of using non-aqueous adhesives instead of aqueous adhesives havebeen proposed.

Non-aqueous adhesives for a polarizing plate that have been proposed sofar may be divided into radical-curable adhesives and cation-curableadhesives depending on the types of curing. Cation-curable adhesiveshave an advantage in that excellent adhesive strength is obtained forfilms made of various materials, but have many disadvantages in themanufacturing process due to a low curing speed and a low degree ofcuring. Radical-curable adhesives having acryl-based compounds oracrylamide-based compounds as a main component have been proposed inorder to solve the problems of such cation-curable adhesives. However,although radical-curable adhesives having acryl-based oracrylamide-based compounds as a main component have a higher curingspeed than cation-curable adhesives, they have problems in that water isused in large quantities due to weak water resistance, and as a result,appearances become poor such that discoloration occurs by the iodideions in a polarizer being affected in a high humidity polarizing platemanufacturing process.

Accordingly, new radical-curable adhesives having excellent waterresistance while having excellent adhesive strength between a polarizerand a protective film have been required.

Meanwhile, in another aspect, display devices having a structure inwhich a polarizing plate is attached to an upper and/or a lowersubstrate of a display panel that generates images using an adhesivehave been generally used, and in order to obtain thin display devices, amethod of laminating a protective film on only one surface of apolarizer using an adhesive, and directly attaching the surface of thepolarizer opposite to the protective film-laminated surface to a displaypanel through an adhesive as a medium without a protective film has beenproposed.

Herein, acryl-based adhesives are normally used as an adhesive used toattach a polarizing plate having the structure described above to adisplay panel. However, as for the acryl-based adhesive, at least athickness of 20 μm is commonly required in order to maintain properadhesive strength, and therefore, there is a problem in that the trendof display devices being thinner and lighter is not satisfied. Inaddition, in the case of acryl-based adhesives, an adhesive layer isgenerally formed using a method of applying an adhesive composition on areleasing film, drying the solvent, and then transferring the result ona sample surface, and this method has disadvantages in that the methodis inconvenient when attaching a polarizing plate to a display device,and productivity decreases. Particularly, the acryl-based adhesivecommonly has a glass transition temperature of 0° C. or less, and whenthis adhesive is directly attached to a polarizer and used, there is aproblem in that heat resistance reliability is reduced, such that cracksoccur in the polarizer in a thermal shock reliability test.

Accordingly, new attaching means capable of being formed to a thin film,improving productivity when attaching a polarizing plate and a displaypanel, and having superior heat resistance reliability has beenrequired.

DISCLOSURE Technical Problem

In view of the above, an object of the present invention is to provide aradical-curable adhesive composition having excellent water resistancewhile having excellent adhesive strength between a polarizer and aprotective film, capable of being formed to a thin film, and capable ofbeing used in attaching a polarizer and a display panel as well as inattaching a polarizer and a protective film, and a polarizing plate andan optical member including the radical-curable adhesive composition.

Technical Solution

In one aspect, the present invention provides a radical-curable adhesivecomposition including a (A) radical-polymerizable compound that includesat least one hydrophilic functional group in the molecule in greaterthan 30 parts by weight and less than or equal to 93 parts by weight; a(B) multifunctional (meth)acryl-based compound in 5 to 40 parts byweight; a (C) phosphate compound that includes one or two (meth)acrylicgroups in the molecule in 1 to 40 parts by weight; and a (D) radicalinitiator in 0.5 to 20 parts by weight, with respect to 100 parts byweight of the radical-curable adhesive composition.

Herein, a total hydroxyl value of the radical-curable adhesivecomposition is preferably 500 to 900 mg KOH/g.

Meanwhile, the hydrophilic functional group of the (A)radical-polymerizable compound is preferably a hydroxyl group.

Meanwhile, the (A) radical-polymerizable compound more preferably uses amixture of a (a-1) radical-polymerizable compound having one hydroxylgroup in the molecule and a (a-2) radical-polymerizable compound havingat least two hydroxyl groups in the molecule.

Meanwhile, the (B) multifunctional (meth)acryl-based compound preferablyincludes one or more types selected from the group consisting ofcompounds represented by the following [Chemical Formula I] to [ChemicalFormula III].

In [Chemical Formula I], R₁ and R₂ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group.

In [Chemical Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxyalkyl group, a hydroxylgroup or a substituted or unsubstituted C₁₋₁₀ alkyl group.

In [Chemical Formula III], R₇ is substituted or unsubstituted C₁₋₁₀alkylene, and R₈ and R₉ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxyalkyl group.

Meanwhile, the (C) phosphate compound is preferably compoundsrepresented by the following [Chemical Formula IV].

In [Chemical Formula IV], R₁₀ is a substituted or unsubstituted C₁₋₁₀alkylene group, a substituted or unsubstituted C₄₋₁₄ cycloalkylenegroup, a substituted or unsubstituted C₆₋₁₄arylene group or acombination thereof; R₁₁ is hydrogen or a methyl group; n is an integerof 1 or 2, m is an integer of 1 or 2 and n+m is 3.

Meanwhile, a thickness of an adhesive layer formed by theradical-curable adhesive composition is preferably 10 μm or less.

In addition, the radical-curable adhesive composition preferably has aglass transition temperature of 50° C. or higher after curing.

Furthermore, the radical-curable adhesive composition preferably hasviscosity of 10 to 300 cP.

In another aspect, the present invention provides a polarizing plateincluding a polarizer; an adhesive layer formed on at least one surfaceof the polarizer; and a polarizer protective film formed on the adhesivelayer, wherein the adhesive layer is formed using the radical-curableadhesive composition.

In still another aspect, the present invention provides an opticalmember including a display panel; and a polarizer attached to anexternal-most surface of the display panel through a medium of anadhesive layer, wherein the adhesive layer is formed using theradical-curable adhesive composition.

Advantageous Effects

A radical-curable adhesive composition according to the presentinvention has excellent adhesive strength for films made of variousmaterials, for example, TAC films, acryl-based films, COP films and PETfilms and the like, and has excellent water resistance such thatdiscoloration of a polarizer does not occur even under high humidityconditions.

Moreover, a radical-curable adhesive composition according to thepresent invention may also be used for attaching a polarizer and adisplay panel, and in this case, it may achieve thinner thickness whencompared to generally-used acryl-based adhesives and the like, and anadhesive layer may be formed between the polarizer and the display panelusing an in-line process, therefore, excellent productivity may beobtained. In addition, the composition has excellent heat resistancereliability compared to generally-used acryl-based adhesives and thelike.

MODE FOR DISCLOSURE

Hereinafter, preferred embodiments of the present invention will bedescribed. However, embodiments of the present invention may be modifiedto various other forms, and the scope of the present invention is notlimited to the embodiments described below. In addition, embodiments ofthe present invention are provided in order to more completely describethe present invention for those having average knowledge in the art.

1. Radical-curable Adhesive Composition

As a result of extensive studies, the inventors of the present inventionhave found that adhesive strength and water resistance are excellentwhen a multifunctional (meth)acryl-based compound, and a phosphatecompound having one or two (meth)acrylic groups in the molecule aremixed to an adhesive composition having a hydrophilic functional groupin a specific content ratio, and completed the present invention.

More specifically, a radical-curable adhesive composition of the presentinvention includes a (A) radical-polymerizable compound that includes atleast one hydrophilic functional group in the molecule in greater than30 parts by weight and less than or equal to 93 parts by weight; a (B)multifunctional (meth)acryl-based compound in 5 to 40 parts by weight; a(C) phosphate compound that includes one or two (meth)acrylic groups inthe molecule in 1 to 40 parts by weight; and a (D) radical initiator in0.5 to 20 parts by weight, with respect to 100 parts by weight of theradical-curable adhesive composition.

1-1. Radical-polymerizable Compound (A)

First, the radical-polymerizable compound included in theradical-curable adhesive composition according to the present inventionis a component for obtaining adhesive strength of an adhesive, andadhesive strength may be obtained through hydrogen bonding by thecompound having at least one hydrophilic functional group in themolecule, and the use of the radical-polymerizable compound is notparticularly limited as long as the compound is capable of radicalpolymerization by the presence of a carbon-carbon unsaturated doublebond in the molecule. Herein, the hydrophilic functional group is notparticularly limited as long as the group is capable of hydrogenbonding, such as a hydroxyl group, a carboxyl group, a urethane group,an amine group and an amide group, however, a hydroxyl group is morepreferable among these for obtaining excellent adhesive strength.

More specifically, examples of the radical-polymerizable compound mayinclude, but are not limited to, compounds represented by the following[Chemical Formula 1] to [Chemical Formula 24]. These may be used eitheralone or as a mixture thereof.

Meanwhile, particularly among these, the radical-polymerizable compoundis, although not limited thereto, preferably used as a mixture of a(a-1) radical-polymerizable compound having one hydroxyl group in themolecule (for example, [Chemical Formula 1] to [Chemical Formula 6] andthe like) and a (a-2) radical-polymerizable compound having at least twohydroxyl groups in the molecule (for example, [Chemical Formula 7] to[Chemical Formula 24] and the like) in terms of obtaining excellentadhesive strength and securing heat resistance.

Meanwhile, the content of the radical-polymerizable compound of thepresent invention may be approximately greater than 30 parts by weightand less than or equal to 93 parts by weight, preferably approximately35 to 90 parts by weight, and more preferably approximately 45 to 90parts by weight, with respect to 100 parts by weight of the wholeadhesive composition. When the content satisfies the above range,excellent adhesive strength may be obtained.

1-2. Multifunctional (Meth)acryl-based Compound (B)

Next, the multifunctional (meth)acryl-based compound included in theradical-curable adhesive composition according to the present inventionis a component for exhibiting stable physical properties even in highhumidity environments by increasing the degree of cross-linkage in anadhesive layer and thereby improving water resistance, and variousmultifunctional (meth)acryl-based compounds widely known in the art maybe used without limit. However, in the present specification, except formultifunctional (meth)acryl-based compounds listed below as examples,compounds corresponding to the (A) compound described above, and the (C)compound to be described later are not included in the multifunctional(meth)acryl-based compound.

In the present invention, examples of the multifunctional(meth)acryl-based compound may include ethylene glycol di(meth)acrylate,1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate,pentaerythritol di(meth)acrylate, ditrimethylolpropane di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropyleneglycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate,silicone di(meth)acrylate, hydroxyl pivalic acid ester neopentyl glycoldi(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxyethoxyethoxycyclohexyl]propane, hydrogen-addeddicyclopentadienyl di(meth)acrylate, tricyclodecane dimethanoldi(meth)acrylate, 1,3-dioxane-2,5-diyl di(meth)acrylate,di(meth)acrylate of2-(2-hydroxy-1,1-dimethylethyl)-5-ethyl-5-hydroxymethyl-1,3-dioxane,tris(hydroxyethyl)isocyanurate di(meth)acrylate, glycerintri(meth)acrylate, trimethylolpropane tri(meth)acrylate,ditrimethylolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, and the like. These may be used either alone or as amixture thereof.

Meanwhile, although not limited thereto, the multifunctional(meth)acryl-based compound more preferably includes one or more typesselected from the group consisting of compounds represented by thefollowing [Chemical Formula I] to [Chemical Formula III]. In this case,water resistance improving effect is more superior.

In [Chemical Formula I], R₁ and R₂ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group.

Herein, in R₁ and R₂, the alkyl of the (meth)acryloyloxyalkyl groupmeans a linear or branched hydrocarbon part of 1 to 10, 1 to 8, or 1 to4 carbon atoms, and the (meth)acryloyloxy group may substitute anyposition of the alkyl group. The rest one or more hydrogen atomsincluded in the alkyl may be substituted with any substituent

In [Chemical Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxyalkyl group, a hydroxylgroup or a substituted or unsubstituted C₁₋₁₀ alkyl group.

Herein, in R₃, R₄, R₅ and R₆, the alkyl of the (meth)acryloyloxyalkylgroup means a linear or branched hydrocarbon part of 1 to 10, 1 to 8, or1 to 4 carbon atoms, and the (meth)acryloyloxy group may substitute anyposition of the alkyl group. The rest one or more hydrogen atomsincluded in the alkyl may be substituted with any substituent.

In addition, in R₆, the alkyl group means a linear or branchedhydrocarbon part of 1 to 10, 1 to 8, or 1 to 4 carbon atoms, and one ormore hydrogen atoms included in the alkyl group may be substituted withany substituent.

In [Chemical Formula III], R₇ is substituted or unsubstituted C₁₋₁₀alkylene, and R₇ and R₈ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxyalkyl group.

Herein, in R₇, the alkylene means a linear or branched divalenthydrocarbon part of 1 to 10, 1 to 8, or 1 to 6 carbon atoms, and thealkylene group in the present specification may include at least oneunsaturated bond in the molecule. Meanwhile, examples of the alkylenegroup may include, but are not limited to, methylene, ethylene,trimethylene, tetramethylene, pentamethylene, hexamethylene,heptamethylene, nonamethylene, decamethylene and the like. One or morehydrogen atoms included in the alkylene may be substituted with anysubstituent. In addition, in R₈ and R₉, the alkyl of the(meth)acryloyloxyalkyl group means a linear or branched hydrocarbon partof 1 to 10, 1 to 8, or 1 to 4 carbon atoms, and the (meth)acryloyloxygroup may substitute any position of the alkyl group. The rest one ormore hydrogen atoms included in the alkyl may be substituted with anysubstituent.

More specifically, the (B) multifunctional (meth)acryl-based compoundparticularly preferably includes, but are not limited to, one or moretypes selected from the group consisting of compounds represented by thefollowing [Chemical Formula 25] to [Chemical Formula 28].

Meanwhile, the content of the multifunctional (meth)acryl-based compoundof the present invention may be approximately 5 to 40 parts by weight,preferably approximately 5 to 35 parts by weight, and more preferablyapproximately 5 to 30 parts by weight, with respect to 100 parts byweight of the whole adhesive composition. When the content of themultifunctional (meth)acryl-based compound is greater than the aboverange, adhesive strength may not be sufficient, and when the content isless than the above range, water resistance may become weak.

1-3. Phosphate Compound (C)

Next, the phosphate compound included in the radical-curable adhesivecomposition according to the present invention is a component forfurther enhancing adhesive strength and water resistance of an adhesive,and various phosphate compounds including one or two (meth)acrylicgroups in the molecule may be used. According to the research results ofthe inventors of the present invention, sufficient adhesive strength andwater resistance are difficult to be secured when only themultifunctional (meth)acryl-based compound is added, and aradical-curable adhesive satisfying both excellent adhesive strength andwater resistance may be prepared when the phosphate compound thatincludes one or two (meth)acrylic groups in the molecule is added at thesame time.

Meanwhile, although not limited thereto, the phosphate compound is morepreferably compounds represented by the following [Chemical Formula IV].In this case, adhesive strength and water resistance improvement effectsof an adhesive are particularly superior.

In [Chemical Formula IV], R₁₀ is a substituted or unsubstituted C₁₋₁₀alkylene group, a substituted or unsubstituted C₄₋₁₄ cycloalkylenegroup, a substituted or unsubstituted C₆₋₁₄ arylene group or acombination thereof; R₁₁ is hydrogen or a methyl group; n is an integerof 1 or 2, m is an integer of 1 or 2 and n+m is 3.

Herein, in R₁₀, the alkylene group means a linear or branched divalenthydrocarbon part of 1 to 10, 1 to 8, or 1 to carbon atoms, and thealkylene group in the present specification may include at least oneunsaturated bond in the molecule. Meanwhile, examples of the alkylenegroup may include, but are not limited to, methylene, ethylene,trimethylene, tetramethylene, pentamethylene, hexamethylene,heptamethylene, nonamethylene, decamethylene and the like. One or morehydrogen atoms included in the alkylene group may be substituted withany substituent.

In addition, in R₁₀, the cycloalkylene group means a nonaromaticdivalent monocyclic, bicyclic or tricyclic hydrocarbon part of 4 to 14,4 to 10, or 4 to 6 ring carbons, and the cycloalkylene group in thepresent specification may include at least one unsaturated bond in themolecule. Meanwhile, examples of the cycloalkylene group may include,but are not limited to, a divalent cyclopentane ring, a divalentcyclohexane ring and the like. One or more hydrogen atoms included inthe cycloalkylene group may be substituted with any substituent.

Furthermore, in R₁₀, the arylene group means a divalent monocyclic,bicyclic or tricyclic aromatic hydrocarbon part having 6 to 14, or 6 to12 ring atoms, and examples thereof may include, but are not limited to,a divalent benzene ring, a divalent naphthalene ring, a divalentanthracene ring, a divalent biphenyl ring and the like. One or morehydrogen atoms included in the arylene group may be substituted with anysubstituent.

Meanwhile, among the groups shown above, R₁₀ is, although not limitedthereto, preferably a substituted or unsubstituted C₁₋₁₀ alkylene group,more preferably a substituted or unsubstituted C₁₋₈ alkylene group, andeven more preferably a substituted or unsubstituted C₁₋₄ alkylene group.

More specifically, although not limited thereto, the phosphate compoundparticularly preferably includes one or more types selected from thegroup consisting of compounds represented by the following [ChemicalFormula 29] to [Chemical Formula 32].

Meanwhile, the content of the phosphate compound of the presentinvention may be approximately 1 to 40 parts by weight, preferablyapproximately 1 to 35 parts by weight, and more preferably approximately1 to 30 parts by weight, with respect to 100 parts by weight of thewhole adhesive composition. When the content of the phosphate compoundis greater than the above range, adhesive strength and a glasstransition temperature may decrease, and when the content is less thanthe above range, water resistance may become weak.

1-4. Radical Initiator (D)

Next, the radical initiator included in the radical-curable adhesivecomposition according to the present invention is for enhancing a curingrate by facilitating radical polymerization. Herein, radical initiatorsgenerally used in the art may be used without limit as the radicalinitiator, and examples thereof may include one or more types selectedfrom the group consisting of 1-hydroxy-cyclohexyl-phenyl-ketone,2-hydroxy-2-methyl-1-phenyl-1-propanone,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, methylbenzoylformate, oxy-phenyl-aceticacid-2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenyl-aceticacid-2-[2-hydroxy-ethoxy]-ethyl ester,alpha-dimethoxy-alpha-phenylacetophenone,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone,diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide, andphenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide. In the presentinvention, phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide isparticularly preferable.

Meanwhile, the content of the radical initiator is preferably, forexample, approximately 0.5 to 20 parts by weight, 0.5 to 15 parts byweight or 0.5 to 10 parts by weight, with respect to 100 parts by weightof the radical-curable adhesive composition. When the content of theradical initiator satisfies the above range, curing of an adhesive maybe smoothly accomplished.

1-5. Physical Properties of Composition

Meanwhile, such a radical-curable adhesive composition of the presentinvention has a total hydroxyl value of approximately 500 to 900 mgKOH/g, preferably approximately 500 to 850 mg KOH/g, and more preferablyapproximately 500 to 800 mg KOH/g. When the hydroxyl value of theradical-curable adhesive composition satisfies the above range, there isan advantage in that an adhesive formed using this composition maystably maintain high adhesive strength with a polarizer even underrather high humidity conditions, and in addition, there is an advantagein that thermal stability may be secured since a high glass transitiontemperature may be obtained due to strong binding power in the curedadhesive.

Meanwhile, the hydroxyl value means a mg number of potassium hydroxide(KOH) required for neutralizing acetic acid bonded to a hydroxyl groupwhen 1 g of a sample is acetylated, and a measurement method is notparticularly limited. For example, the hydroxyl value in the sample maybe calculated through the following Equation (1).

(Molecular Weight of KOH×Number of —OH in Sample×1000)/Molecular Weightof Sample  Equation (1)

In addition, the thickness of an adhesive layer formed by theradical-curable adhesive composition of the present invention may beapproximately greater than 0 and less than or equal to 10 μm, andpreferably approximately 0.1 to 10 μm or 0.1 to 5 μm. When the thicknessof the adhesive layer is less than 0.1 μm, uniformity and adhesivestrength of the adhesive layer may be reduced, and when the thickness ofthe adhesive layer is greater than 10 μm, there may be a problem in thatforming to thin film is difficult, and the exterior of a polarizingplate and the like including the adhesive layer gets wrinkled.

In addition, the radical-curable adhesive composition according to thepresent invention may have a glass transition temperature of 50° C. orhigher after curing, for example, 80 to 300° C. or 90 to 200° C. Apolarizing plate prepared using the radical-curable adhesive compositionaccording to the present invention having a glass transition temperaturein the range described above has an advantage in that heat resistanceand water resistance are excellent.

Furthermore, the radical-curable adhesive composition according to thepresent invention preferably has viscosity of approximately 10 to 300cP, or 20 to 100 cP. When the viscosity of the adhesive compositionsatisfies the above range, there is an advantage in that the adhesivelayer may be formed to be thin, and workability is excellent due to lowviscosity of the adhesive layer.

Meanwhile, the radical-curable adhesive composition of the presentinvention described above may be very favorably used for a polarizingplate since the composition has excellent water resistance while havingexcellent adhesive strength for films made of various materials.

In addition, the radical-curable adhesive composition of the presentinvention described above may also exhibit excellent adhesive strengthbetween a polarizer and a display panel, may form an adhesive layer as athin film, has excellent heat resistance reliability, and furthermore,has excellent productivity in that the adhesive layer may be formedbetween the polarizer and the display panel using an in-line process,and therefore, the radical-curable adhesive composition of the presentinvention may also be favorably used when directly attaching a polarizerto a display panel.

Hereinafter, a polarizing plate and an optical member including theradical-curable adhesive composition of the present invention will bespecifically described.

2. Polarizing Plate

First, a polarizing plate according to the present invention will bedescribed.

A polarizing plate of the present invention includes a polarizer; anadhesive layer formed on at least one surface of the polarizer; and aprotective film formed on the adhesive layer, wherein the adhesive layeris formed using the radical-curable adhesive composition of the presentinvention described above.

2-1. Polarizer

First, the polarizer is not particularly limited, and polarizers wellknown in the art, for example, films formed with polyvinyl alcohol (PVA)including iodine or dichroic dye may be used. The polarizer may beprepared by dyeing a PVA film with iodine or dichroic dye, however, thepreparation method is not particularly limited. In the presentspecification, a polarizer means a state not including a protectivefilm, and a polarizing plate means a state including a polarizer and aprotective film.

2-2. Adhesive Layer

Next, the adhesive layer is formed using the radical-curable adhesivecomposition according to the present invention described above, and maybe formed using methods well known in the art. For example, a method offorming an adhesive layer by applying an adhesive composition on onesurface of a polarizer or a protective film, laminating the polarizerand the protective film, and then curing the result may be used. Herein,the application may be carried out using coating methods well known inthe art, such as spin coating, bar coating, roll coating, gravurecoating, and blade coating.

Meanwhile, the curing may be carried out by photocuring, morespecifically, irradiating active energy rays such as ultraviolet rays,visible rays, an electron beam and X-rays. For example, the curing maybe carried out using a method of irradiating ultraviolet rays ofapproximately 10 to 2500 mJ/cm² using an ultraviolet ray irradiator(metal halide lamp).

Alternatively, the curing may also be carried out by heat curing, morespecifically, heat curing at a curing temperature of 80° C. or higher.Herein, in the heat curing, a known amine-based initiator may beadditionally added to the composition as necessary for increasing thecuring speed.

In addition, as the curing, the heat curing may be additionally carriedout after the photocuring, or the photocuring may be additionallycarried out after the heat curing.

2-3. Protective Film

Next, the protective film is used for supporting and protecting apolarizer, and protective films made of various materials generallyknown in the art, such as cellulose-based films, polyethyleneterephthalate (PET) films, cycloolefin polymer (COP) films andacryl-based films, may be used without limit. Among these, using anacryl-based film is particularly preferable considering opticalproperties, durability, economic efficiency and the like.

Meanwhile, an acryl-based film capable of being used in the presentinvention may be obtained by extrusion molding materials to be moldedincluding a (meth)acrylate-based resin as a main component. Herein, the(meth)acrylate-based resin is a material having a resin including a(meth)acrylate-based unit as a main component, and the concept alsoincludes not only a homopolymer resin formed with a (meth)acrylate-basedunit, but also a copolymer resin copolymerizing other monomer units inaddition to a (meth)acrylate-based unit, and a blend resin blendingother resins to such a (meth)acrylate-based resin.

Meanwhile, the (meth)acrylate-based unit may be, for example, analkyl(meth)acrylate-based unit. Herein, the alkyl(meth)acrylate-basedunit means both an alkylacrylate-based unit and analkylmethacrylate-based unit, and the alkyl group of thealkyl(meth)acrylate-based unit preferably has a carbon number of 1 to10, and more preferably has a carbon number of 1 to 4.

In addition, the monomer unit capable of being copolymerized with the(meth)acrylate-based unit may include a styrene-based unit, a maleicanhydride-based unit, a maleimide-based unit and the like. Herein,examples of the styrene-based unit may include, but are not limited to,styrene, α-methylstyrene and the like; examples of the maleicanhydride-based monomer may include, but are not limited to, maleicanhydride, methyl maleic anhydride, cyclohexyl maleic anhydride, phenylmaleic anhydride and the like; and examples of the maleimide-basedmonomer may include, but are not limited to, maleimide,N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide and thelike. These may be used either alone or as a mixture.

Meanwhile, the acryl-based film may be a film including a(meth)acrylate-based resin having a lactone ring structure. Specificexamples of the (meth)acrylate-based resin having a lactone ringstructure may include a (meth)acrylate-based resin having a lactone ringstructure disclosed in Japanese Patent Application Laid-Open PublicationNo. 2000-230016, Japanese Patent Application Laid-Open Publication No.2001-151814 and Japanese Patent Application Laid-Open Publication No.2002-120326, and the like.

A method for preparing the acryl-based film is not particularly limited,and for example, the acryl-based film may be prepared by preparing athermoplastic resin composition by sufficiently mixing a(meth)acrylate-based resin, other polymers, additives and the like usingany proper mixing method, and then molding the result to a film, or theacryl-based film may be prepared by preparing a (meth) acrylate-basedresin, other polymers, additives and the like as a separate solution,then forming a uniformly mixed solution by mixing the separatelyprepared solutions, and molding the result to a film. In addition, theacryl-based film may be any one of an unoriented film or an orientedfilm. When the acryl-based film is an oriented film, it may be either amonoaxially oriented film or a biaxially oriented film, and when theacryl-based film is a biaxially oriented film, it may be any one of asimultaneous biaxially oriented film or a sequential biaxially orientedfilm.

Meanwhile, the polarizing plate of the present invention may furtherinclude a primer layer in between the adhesive layer and the protectivefilm for further improving adhesive strength. Herein, the primer layermay be formed using a method of applying a coating solution including awater dispersible polymer resin, water dispersible fine particles andwater on the protective film using a bar coating method, a gravurecoating method or the like, and drying the result. Examples of the waterdispersible polymer resin may include a water dispersiblepolyurethane-based resin, a water dispersible acryl-based resin, a waterdispersible polyester-based resin or a combination thereof, and as thewater dispersible fine particles, inorganic-based fine particles such assilica, titania, alumina and zirconia, organic-based fine particlesformed with a silicone-based resin, a fluorine-based resin, a(meth)acryl-based resin, a cross-linked polyvinyl alcohol and amelamine-based resin, or a combination thereof, may be used, but theexamples are not limited thereto.

3. Optical Member

Next, an optical member according to the present invention will bedescribed.

An optical member of the present invention includes a display panel; anda polarizer attached to an external-most surface of the display panelthrough a medium of an adhesive layer, wherein the adhesive layer isformed using the radical-curable adhesive composition of the presentinvention described above.

3-1. Display Panel

First, a display panel capable of being used in the present invention isnot particularly limited, and for example, various modes of liquidcrystal panels used in liquid crystal display devices may be used.Herein, specific constitutions of the liquid crystal panel are notparticularly limited, and for example, the constitution may includeupper transparent substrate/color filter/protective film/transparentconductive film electrode/oriented film/liquid crystal/orientedfilm/thin film transistor/lower transparent substrate, and the like.

The optical member of the present invention may have a polarizerattached to the external-most surface, that is, an upper transparentsubstrate or a lower transparent substrate, of a display panel through amedium of an adhesive layer, and herein, the adhesive layer is formedusing the radical-curable adhesive composition of the present inventiondescribed above. Meanwhile, materials of the transparent substrate towhich a polarizer is attached through a medium of an adhesive layer arenot particularly limited, and known glass substrates or transparentpolymer films may be used without limit.

3-2. Polarizer

Next, the polarizer is not particularly limited as described above, andpolarizers well known in the art, for example, films formed withpolyvinyl alcohol (PVA) including iodine or dichroic dye may be used. Inaddition, as described above, the polarizer may be prepared by dyeing aPVA film with iodine or dichroic dye, however, the preparation method isnot particularly limited thereto.

Meanwhile, the polarizer may attach a separate protective film on thesurface opposite to the surface attached to a display panel through amedium of an adhesive layer in order for supporting and protecting thepolarizer. Herein, the details of the protective film are the same asthose described above.

Meanwhile, attaching the polarizer and the protective film may becarried out using a method of applying an adhesive on the surface of thepolarizer or the protective film using a roll coater, a gravure coater,a bar coater, a knife coater or a capillary coater and the like, andthen laminating the result with heat using a laminating roll, orlaminating by pressing the result at room temperature, or irradiating UVafter laminating the result, or the like. Meanwhile, the adhesive is notlimited to the radical-curable adhesive of the present inventiondescribed above, and various adhesives for a polarizing plate used inthe art, such as a polyvinyl alcohol-based adhesive, apolyurethane-based adhesive, an acryl-based adhesive, and a cation-basedor radical-based adhesive may be used without limit.

3-3. Adhesive Layer

Next, the adhesive layer is formed using the radical-curable adhesivecomposition of the present invention described above, and may be formedthrough an in-line process well known in the art. Specifically, theformation of the adhesive layer may be carried out using, for example, amethod in which the radical-curable adhesive composition of the presentinvention is applied on the surface of a polarizer using a coatingmethod well known in the art, while unwiding the polarizer or apolarizing plate in which a protective film is attached to one surfaceof the polarizer from a roll, then laminating the result on a displaypanel, and curing the coated adhesive composition layer. Herein, thecuring may be carried out by photocuring as described above. Theadhesive layer of the present invention may be formed through an in-lineprocess as described above, and therefore, has an advantage in thatproductivity is excellent such that continuous production may beobtained.

Meanwhile, the adhesive layer may have a thickness of approximately 10μm or less, and preferably approximately 0.1 to 10 μm or 0.1 to 5 μm. Asfor existing acryl-based adhesives commonly used for attaching apolarizer (or polarizing plate) to a display panel, at least a thicknessof 20 μm is required in order to maintain proper adhesive strength,therefore, manufacturing thin display devices including this adhesivehas had a limit, however, the adhesive layer of the present inventionmay be formed to be thin as described above, and therefore, there is anadvantage in that display devices including this adhesive layer may bemanufactured to be thinner.

Hereinafter, the present invention will be described in more detail withreference to specific examples.

Preparation Example 1 Preparation of Acryl-based Protective Film

Raw material pellets were prepared by supplying a resin compositionobtained by uniformly mixingpoly(N-cyclohexylmaleimide-co-methylmethacrylate), a styrene-maleicanhydride copolymer resin and a phenoxy-based resin in a weight ratio of100:2.5:5 to a 24φ extruder substituted with nitrogen from a rawmaterial hopper to an extruder, and melting the result at 250° C.

As the phenoxy-based resin, PKFE (Mw=60,000, Mn=16,000, Tg=95° C.)manufactured by InChem Corporation (InChemRez) was used. As thestyrene-maleic anhydride copolymer resin, Dylaeck 332 that is 85% byweight of styrene and 15% by weight of maleic anhydride was used, and asthe poly(N-cyclohexylmaleimide-co-methylmethacrylate) resin, a compoundhaving the N-cyclohexylmaleimide content in 6.5% by weight when analyzedusing an NMR was used.

The obtained raw material pellets were vacuum dried, were melted at 260°C. using an extruder, then passed through a coat-hanger-type T-die, andthen passed through a chrome plating casting roll and a drying roll, andas a result, a film having a thickness of 150 μm was prepared. Anacrylic film was prepared by orienting this film to a percentage of 170%in an MD direction at 125° C. using the speed difference of the rollswith a pilot orientation apparatus.

The acrylic film prepared through the process described above was coronatreated, and a primer composition, in which 20 parts by weight of anoxazoline cross-linking agent (manufactured by Nippon Shokubai Co. Ltd.,WS700) was added to a primer composition having a solid content of 10%by weight prepared by diluting CK-PUD-F (urethane dispersionmanufactured by Chokwang Paint Ltd.) with pure water, was coated on onesurface of the acrylic film using a #7 bar, and the result was orientedto a percentage of 190% in a TD direction at 130° C. using a tenter, andfinally, an acryl-based protective film having a primer layer thicknessof 400 nm was prepared.

Preparation Example 2 Preparation of Adhesive Composition

(1) Adhesive Composition A

Adhesive Composition A for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 64.5% byweight, hydroxyethyl acrylate (HEA) in 16.1% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 16.1% by weight anddi-(methacryloyloxy ethyl)phosphate in 3.3% by weight.

(2) Adhesive Composition B

Adhesive Composition B for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 56.5% byweight, hydroxyethyl acrylate (HEA) in 24.2% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 16.1% by weight anddi-(methacryloyloxy ethyl)phosphate in 3.2% by weight.

(3) Adhesive Composition C

Adhesive Composition C for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 32.3% byweight, glyceryl methacrylate (GLM) in 32.3% by weight, hydroxyethylacrylate (HEA) in 16.1% by weight, dimethylol tricyclodecane diacrylate(DCPDA) in 16.1% by weight and di-(methacryloyloxy ethyl)phosphate in3.2% by weight.

(4) Adhesive Composition D

Adhesive Composition D for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 16.1% byweight, glyceryl methacrylate (GLM) in 48.4% by weight, hydroxyethylacrylate (HEA) in 16.1% by weight, dimethylol tricyclodecane diacrylate(DCPDA) in 16.1% by weight and di-(methacryloyloxy ethyl)phosphate in3.3% by weight.

(5) Adhesive Composition E

Adhesive Composition E for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 55.5% byweight, hydroxyethyl acrylate (HEA) in 13.9% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 27.8% by weight anddi-(methacryloyloxy ethyl)phosphate in 2.8% by weight.

(6) Adhesive Composition F

Adhesive Composition F for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 72.6% byweight, hydroxyethyl acrylate (HEA) in 8.1% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 16.1% by weight anddi-(methacryloyloxy ethyl)phosphate in 3.2% by weight.

(7) Adhesive Composition G

Adhesive Composition G for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 31.2% byweight, hydroxyethyl acrylate (HEA) in 7.8% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 30.5% by weight anddi-(methacryloyloxy ethyl)phosphate in 30.5% by weight.

(8) Adhesive Composition H

Adhesive Composition H for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding hydroxyethyl acrylate (HEA) in 96% byweight, dimethylol tricyclodecane diacrylate (DCPDA) in 3.3% by weightand di-(methacryloyloxy ethyl)phosphate in 0.7% by weight.

(9) Adhesive Composition I

Adhesive Composition I for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding hydroxyethyl acrylamide (HEAA) in 64.5%by weight, hydroxyethyl acrylate (HEA) in 16.1% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 16.1% by weight anddi-(methacryloyloxy ethyl)phosphate in 3.3% by weight.

(10) Adhesive Composition J

Adhesive Composition J for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 43.4% byweight, hydroxyethyl acrylate (HEA) in 11.3% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 43% by weight anddi-(methacryloyloxy ethyl)phosphate in 2.3% by weight.

(11) Adhesive Composition K

Adhesive Composition K for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 73.8% byweight, hydroxyethyl acrylate (HEA) in 18.5% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 4% by weight anddi-(methacryloyloxy ethyl)phosphate in 3.7% by weight.

(12) Adhesive Composition L

Adhesive Composition L for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 37.4% byweight, hydroxyethyl acrylate (HEA) in 9.8% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 9.8% by weight anddi-(methacryloyloxy ethyl)phosphate in 43% by weight.

(13) Adhesive Composition M

Adhesive Composition M for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 66.1% byweight, hydroxyethyl acrylate (HEA) in 16.5% by weight, dimethyloltricyclodecane diacrylate (DCPDA) in 16.5% by weight anddi-(methacryloyloxy ethyl)phosphate in 0.9% by weight.

(14) Adhesive Composition N

Adhesive Composition N for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 76% byweight, hydroxyethyl acrylate (HEA) in 19% by weight anddi-(methacryloyloxy ethyl)phosphate in 5% by weight.

(15) Adhesive Composition O

Adhesive Composition O for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding glyceryl monoacrylate (GLA) in 66.7% byweight, hydroxyethyl acrylate (HEA) in 16.65% by weight and dimethyloltricyclodecane diacrylate (DCPDA) in 16.65% by weight.

(16) Adhesive Composition P

Adhesive Composition P for a polarizing plate was prepared by adding 3parts by weight of irgacure-819 (manufactured by Ciba SpecialtyChemicals Inc.), a radical initiator, to 100 parts by weight of a resincomposition prepared by adding hydroxyethyl acrylate (HEA) in 80.6% byweight, dimethylol tricyclodecane diacrylate (DCPDA) in 16.1% by weightand di-(methacryloyloxy ethyl)phosphate in 3.3% by weight.

Example 1

The Adhesive Composition A was applied on the primer layer of theacrylic film-based protective film prepared in Preparation Example 1using a dropping pipette, and the result was laminated on both surfacesof a polarizer (PVA element), and then the result passed through alaminator (5 m/min) after setting the condition of the adhesive layer tohave a final thickness of 1 to 2 μm. Next, ultraviolet rays of 1000mJ/cm² irradiated on the surface laminated with the acrylic film using aUV irradiator (metal halide lamp), and as a result, a polarizing platewas prepared. Meanwhile, the polarizing plate was prepared under acondition of a temperature of 20° C. and humidity of 50%.

Example 2

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition B was used.

Example 3

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition C was used.

Example 4

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition D was used.

Example 5

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition E was used.

Example 6

A polarizing plate was prepared in the same manner as in

Example 1 except that Adhesive Composition F was used.

Comparative Example 1

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition G was used.

Comparative Example 2

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition H was used.

Comparative Example 3

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition I was used.

Comparative Example 4

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition J was used.

Comparative Example 5

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition K was used.

Comparative Example 6

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition L was used.

Comparative Example 7

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition M was used.

Comparative Example 8

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition N was used.

Comparative Example 9

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition O was used.

Comparative Example 10

A polarizing plate was prepared in the same manner as in Example 1except that Adhesive Composition P was used.

Test Example 1—Hydroxyl Value

The hydroxyl value of the adhesive composition used in the examples andthe comparative examples was measured and shown in the following [Table1]. Herein, the hydroxyl value of the adhesive composition wascalculated using the following Equation (1).

(Molecular Weight of KOH×Number of —OH in Sample×1000)/Molecular Weightof Sample  Equation (1)

Test Example 2—Evaluation on Peel Strength of Polarizing Plate

Peel strength of the polarizing plate prepared in the examples and thecomparative examples was measured, and shown in the following [Table 1].Specifically, the polarizing plate prepared in the examples and thecomparative examples was left unattended for 4 days under a condition ofa temperature of 20° C. and humidity of 70%, then cut into pieces havinga width of 20 mm, and a length of 100 mm, and the peel strength of thepolarizer and the protective film was measured at a speed of 300 m/minand 90 degrees using a texture analyzer apparatus (TA-XT Plusmanufactured by Stable Micro Systems, Ltd.). Herein, the peel strengthof 2.5 N/2 cm or greater was marked as ⊚, the peel strength of greaterthan or equal to 1.5 N/2 cm and less than 2.5 N/2 cm was marked as ∘,the peel strength of greater than or equal to 1.0 N/2 cm and less than1.5 N/2 cm was marked as X, and the peel strength of less than 1.0 N/2cm was marked as XX.

Test Example 3—Evaluation on Water Resistance of Polarizing Plate

Water resistance of the polarizing plate prepared in the examples andthe comparative examples was measured and shown in the following [Table2]. Specifically, the polarizing plate of the examples and thecomparative examples was laminated on a glass substrate, and thenimmersed in a thermostat at 60° C., and water resistance was determinedafter 8 hours by the discoloration at the end of the polarizing plate,and when there was no discoloration, it was marked as excellent, andwhen there was discoloration, it was marked as poor.

TABLE 1 Adhesive hydroxyl value Peel Water Category Composition[mgKOH/g] Strength Resistance Example 1 A 591 ⊚ Excellent Example 2 B568 ⊚ Excellent Example 3 C 569 ⊚ Excellent Example 4 D 558 ⊚ ExcellentExample 5 E 508 ⊚ Excellent Example 6 F 614 ⊚ Excellent Comparative G440 XX Excellent Example 1 Comparative H 686 ⊚ Poor Example 2Comparative I 412 XX Poor Example 3 Comparative J 416 XX Poor Example 4Comparative K 676 ◯ Poor Example 5 Comparative L 569 ◯ Poor Example 6Comparative M 537 ⊚ Poor Example 7 Comparative N 702 ⊚ Poor Example 8Comparative O 593 ◯ Poor Example 9 Comparative P 389 XX Poor Example 10

As shown in Table 1, in Examples 1 to 6 of the present invention, it wasseen that excellent water resistance was obtained in addition toexcellent adhesive strength.

Meanwhile, in Comparative Examples 1 to 7 having the content of the (A)to (C) compounds outside the ranges proposed in the present invention,it was seen that adhesive strength was reduced, or water resistance wasweak, or both.

In addition, in Comparative Example 8 that does not include the (B)compound, it was seen that water resistance was weak, and in ComparativeExample 9 that does not include the (C) compound, it was also seen thatwater resistance was weak.

Furthermore, in Comparative Example 3 using a phosphate compound havingthree acryloyl groups as the (C) compound, it was seen that bothadhesive strength and water resistance were poor.

Example 7

The Adhesive Composition A was applied on a glass substrate, and apolarizer (PVA element) and an upper protective film were laminatedthereon, and then the result passed through a laminator (5 m/min) aftersetting the condition of the adhesive layer to have a final thickness of1 to 2 μm. Next, ultraviolet rays of 1000 mJ/cm² irradiated on thesurface laminated with the polarizer and the protective film using a UVirradiator (metal halide lamp), and as a result, an optical member inwhich the polarizer is attached to the glass substrate was prepared.Meanwhile, the optical member was prepared under a condition of atemperature of 20° C. and humidity of 50%.

Test Example 4—Evaluation on Peel Strength of Optical Member

Peel strength of the polarizing plate prepared in Example was measured,and shown in the following [Table 2]. Specifically, the optical memberprepared in Example 7 was left unattended for 4 days under a conditionof a temperature of 20° C. and humidity of 70%, then cut into pieceshaving a width of 20 mm, and a length of 100 mm, and the peel strengthof the polarizer and the glass substrate was measured at a speed of 300m/min and 90 degrees using a texture analyzer apparatus (TA-XT Plusmanufactured by Stable Micro Systems, Ltd.). Herein, the peel strengthof 2.0 N/2 cm or greater was marked as excellent, the peel strength ofgreater than or equal to 1.0

N/2 cm and less than 2.0 N/2 cm was marked as fair, and the peelstrength of less than 1.0 N/2 cm was marked as poor. Meanwhile, a methodfor measuring the hydroxyl value additionally listed in the followingTable 2 is the same as the method described above.

TABLE 2 Adhesive Hydroxyl Value Peel Water Category Composition [mgKOH/g] Strength Resistance Example 7 A 591 Excellent Excellent

As shown in Table 2, it was seen that the adhesive composition of thepresent invention also has excellent adhesive strength between thepolarizer and the glass substrate.

Hereinbefore, examples of the present invention have been described indetail, however, claims of the present invention are not limitedthereto, and it will be apparent to those skilled in the art thatvarious modifications and changes may be made without departing from thespirit of the present invention described in the claims.

1. A radical-curable adhesive composition comprising: a (A)radical-polymerizable compound that includes at least one hydrophilicfunctional group in the molecule in greater than 30 parts by weight andless than or equal to 93 parts by weight; a (B) multifunctional(meth)acryl-based compound in 5 to 40 parts by weight; a (C) phosphatecompound that includes one or two (meth)acrylic groups in the moleculein 1 to 40 parts by weight; and a (D) radical initiator in 0.5 to 20parts by weight, with respect to 100 parts by weight of theradical-curable adhesive composition.
 2. The radical-curable adhesivecomposition of claim 1, which has a total hydroxyl value of 500 to 900mg KOH/g.
 3. The radical-curable adhesive composition of claim 1,wherein the hydrophilic functional group of the (A)radical-polymerizable compound is a hydroxyl group.
 4. Theradical-curable adhesive composition of claim 3, wherein the (A)radical-polymerizable compound is a mixture of a (a-1)radical-polymerizable compound having one hydroxyl group in the moleculeand a (a-2) radical-polymerizable compound having at least two hydroxylgroups in the molecule.
 5. The radical-curable adhesive composition ofclaim 1, wherein the (B) multifunctional (meth)acryl-based compoundincludes one or more types selected from the group consisting ofcompounds represented by the following [Chemical Formula I] to [ChemicalFormula III]:

wherein, in [Chemical Formula I], R₁ and R₂ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group;

in [Chemical Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group or a (meth)acryloyloxyalkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxyalkyl group, a hydroxylgroup or a substituted or unsubstituted C₁₋₁₀ alkyl group; and

in [Chemical Formula III], R₇ is substituted or unsubstituted C₁₋₁₀alkylene, and R₈ and R₉ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxyalkyl group.
 6. The radical-curable adhesivecomposition of claim 1, wherein the (C) phosphate compound includes acompound represented by the following [Chemical Formula IV]:

wherein, in [Chemical Formula IV], R₁₀ is a substituted or unsubstitutedC₁₋₁₀ alkylene group, a substituted or unsubstituted C₄₋₁₄ cycloalkylenegroup, a substituted or unsubstituted C₆₋₁₄ arylene group or acombination thereof; R₁₁ is hydrogen or a methyl group; n is an integerof 1 or 2, m is an integer of 1 or 2 and n+m is
 3. 7. Theradical-curable adhesive composition of claim 1, wherein a thickness ofan adhesive layer formed by the radical-curable adhesive composition is10 μm or less.
 8. The radical-curable adhesive composition of claim 1,which has a glass transition temperature of 50° C. or higher aftercuring.
 9. The radical-curable adhesive composition of claim 1, whichhas viscosity of 10 to 300 cP.
 10. A polarizing plate comprising: apolarizer; an adhesive layer formed on at least one surface of thepolarizer; and a polarizer protective film formed on the adhesive layer;wherein the adhesive layer is formed using the radical-curable adhesivecomposition of claims
 1. 11. An optical member comprising: a displaypanel; and a polarizer attached to an external-most surface of thedisplay panel through a medium of an adhesive layer; wherein theadhesive layer is formed using the radical-curable adhesive compositionof claim 1.